Colorectal cancer is the second most common visceral malignancy in the United States among men and women. The biology of colorectal cancer provides unique opportunities for etiologic research. Colorectal cancer appears to arise from a series of precursor lesions. By studying these precursors, epidemiologists can identify important clues to colon cancer etiology and progression. Increased rectal mucosal proliferation appears to be an early step in the colon cancer sequence. The proposed study is designed to examine demographic and environmental factors associated with increased mucosal proliferative index. The study should substantially increase our understanding of the epidemiology of rectal mucosal proliferation. Such knowledge will improve our understanding of the carcinogenic process and permit us to develop rational intervention studies. The study is a competing continuation of research designed to determine risk factors for colon adenomas and employs similar methods and personnel. The specific aims of the proposed study are: to characterize rectal mucosal proliferative labelling index using bromodeoxyuridine and proliferating cell nuclear antigen; to determine the association between rectal mucosal proliferative index and the presence of colon adenomas and cancer; and, to determine the association between rectal mucosal proliferative index and specific dietary factors and lifestyle factors that have been associated with colorectal cancer. Study subjects will be 500 consenting male and female patients at the University of North Carolina Hospitals who meet study eligibility criteria. Rectal mucosal pinch biopsies will be taken from subjects during routine colonoscopy and immediately processed. Proliferative labelling index will be determined using bromodeoxyuridine and proliferating nuclear cell antigen. Patients will be interviewed by a trained nutritionist about dietary intake using a standard semi-quantitive food frequency questionnaire and about a number of lifestyle and environmental factors. Pathologic material will be reviewed by a single pathologist to determine type of polyp, degree of atypia, and presence of cancer. Data analysis will compare proliferative indices in various demographic and exposure strata.